Actinide Nanoparticle Research

Actinide Nanoparticle Research

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Stepan N. Kalmykov Melissa A. Denecke l

Editors

Actinide Nanoparticle Research

Editors Prof.Dr. Stepan N. Kalmykov Lomonosov Moscow State University Dept. Chemistry Leninskie Gory 1/3 119991 Moscow Russia [email protected]

Dr. Melissa A. Denecke Forschungszentrum Karlsruhe Inst. Nukleare Entsorgungstechnik Postfach 36 40 76021 Karlsruhe Germany [email protected]

ISBN 978-3-642-11431-1 e-ISBN 978-3-642-11432-8 DOI 10.1007/978-3-642-11432-8 Springer Heidelberg Dordrecht London New York Library of Congress Control Number: 2011924898 # Springer-Verlag Berlin Heidelberg 2011 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer. Violations are liable to prosecution under the German Copyright Law. The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Cover design: eStudio Calamar S.L. Printed on acid-free paper Springer is part of Springer ScienceþBusiness Media (www.springer.com)

Foreword

A challenge for most of the countries that developed nuclear fuel cycles is the problem of safe and economically reasonable methods for management of spent nuclear fuel (SNF) and radioactive wastes. In Russia, the government plans to increase the share of nuclear power from 15% up to 25% by 2030. This would increase the volume of SNF that have to be processed and nuclear wastes that have to be disposed into the geological repositories. On these grounds, research in different fields including behavior of SNF and vitrified nuclear wastes under repository conditions, interaction of radionuclides with engineered and natural barriers, migration and speciation of radionuclides in the environment, and so on, is highly appreciated. Another challenging problem that many countries face is the remediation of contaminated sites as a legacy of such diverse activities as weapon programs, SNF reprocessing, or uranium mining and milling. No effective remediation strategies could be developed without knowledge on the speciation of radionuclides. It was demonstrated by research groups in many countries that actinides, as well as other radionuclides, tend to form colloid particles of different nature that are responsible for their environmental behavior. Structurally, most of these colloids are hierarchic particles that consist of agglomerated nanoparticles. In order to understand and predict their environmental behavior, their characterization at nano- and subnano scale is required. This is the first book that covers different aspects of actinide nanoresearch: formation, structure, and properties of actinide nanoparticles and thin layers, environmental behavior of actinide colloids including modeling approaches. Several chapters are devoted to the new innovative spectroscopic and microscopic techniques of actinide nanoparticle characterization. This book is of interest both for fundamental research into chemistry and physics of actinides and for applied researchers. The chapters are written and reviewed by top-level specialists in the field of actinide chemistry, allowing one to recommend this book to broad audience including scientists, engineers, and students who study nuclear chemistry. Moscow, Russia February 2011

Boris F. Myasoedov Academician, Professor, Honorary chairman of Russian-German Symposium on Actinide Nanoparticles v

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Preface

The idea for this book on actinide nanoparticle research was born during the “Russian–German Symposium on Actinide Nanoparticles” held in May 2009 in Moscow and organized by the institutes Department of Chemistry of the Lomonosov Moscow State University (MSU) and the Institute of Nuclear Waste Disposal at the Karlsruhe Institute of Technology (KIT-INE). The symposium itself is a milestone in a cooperation between MSU and KIT-INE, the Helmholtz-Russian Joint Research Group entitled “Actinide Nanoparticles: Formation, Stability, and Properties Relevant to the Safety of Nuclear Waste Disposal” funded by the German Helmholtz Society and the Russian Foundation for Basic Research. The research interest in actinide nanoparticles is multifaceted. An obvious interest lies in their importance for safety research related to nuclear waste disposal and assessment of actinide-contaminated sites, as the formation and transport of actinide nanoparticles is an environmental concern that is vital not only to our generation but also to future generations. There are other aspects of more basic character, which are a driving force behind actinide nanoparticle research. This research belongs to a distinct realm of nanoscience, but with a history longer than other areas of today’s conventional nanoscience. Modern nanoscience, as a presently well-funded, “sexy” research area, has actually joined the ranks of the area of nanoscience referred to for decades as colloid chemistry or colloid research, including macro- and supramolecular chemistry. Our endeavors in actinide nanoparticle research entail much more than being simply classified as a sector of nanoscience, however. We are clearly tackling the grand challenge of understanding the behavior of these heavy elements as nanoclusters and nanoparticles with inherent special behavior, reactivity, and structure. Part of this challenge lies in the radioactivity of actinide-containing systems investigated, requiring specialized expertise and infrastructure. It is not always a trivial task equipping instrumentation for nanoparticle characterization to make safe studies of radioactive systems possible and only a limited number of laboratories worldwide have the capability and licensing for working with transuranium actinide elements. Certainly an exceptionally challenging aspect is the

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theoretical description of heavy actinide elements. Experimental observation and interpretation on the nanoscale is driving instrumentation and method development and the thrust to couple experiments on actinide systems with quantum chemical calculations is promoting advances in theory. Theoretical, computational description of 5f element systems must deal with numerous electrons in (5f, 6d, 7s, and 6p) orbitals close in energy, requiring scalar and often spin-orbit relativistic effects or electron correlation effects. Many chapters of this book, but not all, are an extension or overview of presentations given at the Russian–German Symposium on Actinide Nanoparticles. The first chapter Actinide Nanoparticles – Generation, Stability, and Mobility is a summary of the presentation given by Professor Horst Geckeis at the symposium and is an excellent discourse on the state of knowledge and the importance of environmental actinide nanoparticle behavior. The remaining chapters of this book are divided into four sections dealing with different aspects of actinide nanoparticle research, in a manner similar to the structure of the symposium: Methods, Modeling, Surface Reactivity and Environmental Behavior. In the Methods section, we have included imaging, spectroscopic and separation techniques covering overviews of previous studies (STXM, FFF, and MS), newer results (STEM), and a chapter on a newer spectroscopy offering great potential for direct characterization of actinide nanoparticle bulk electronic structure (RIXS). The Modeling section includes not only a treatise on modeling of colloid-mediated actinide transport in the environment but also a chapter on the outlook of quantum chemical strategies for computing actinide nanoparticle structures. This is followed by a section on Interfacial Phenomena and Formation of Actinide Nanoparticles. The interfacial phenomena are addressed in three separate chapters, one reporting new results from an investigation of actinide ion interaction with silica nanoparticles, the second chapter on well-defined thin films produced under controlled sputtering conditions as models for reactive surfaces, especially spent fuel but potentially applicable for advancing our understanding of actinide nanoparticles with inherent large surface to bulk ratios. The third chapter in this section deals with novel structures of uranium selenate clusters, which can serve as models for formation and reactivity of certain classes of actinide nanoparticles. The last section presents results from previous and new investigations of actinide nanoparticle environmental behavior. Four of this section’s chapters deal with anthropogenic actinide contamination legacies; the last chapter reports new results of X-ray tomography investigations with nanoscale resolution and techniques offering a potentially encouraging outlook for future research activities. Ultimate goal in actinide nanoparticle research of attaining a level of understanding, which permits us to predict and ultimately control actinide behavior in systems covering the entire size-scale range – from ion, to nanoclusters, to nanoparticles and microparticles, up to bulk, condensed systems – is not only a noble ambition necessary for providence of modern society, it is at the forefront of research. Potential applications include synthesis of actinide systems targeted toward novel structures, as well as selected chemical and physical characteristics, and reliable prediction of actinide mobility in geochemical milieus on a long-term

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timescale necessary for safety assessment of nuclear waste disposal concepts and strategies for eliminating/minimizing risks associated with contamination legacies. This is indeed a grand challenge. This humble endeavor, as the first book published on the subject of actinide nanoparticle research, represents one step in our exciting journey into the fascinating domain of the multifarious actinide nanoscopic world. Karlsruhe, Germany Moscow, Russia February 2011

Melissa A. Denecke Stepan N. Kalmykov

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Contents

Actinide-Nanoparticle Interaction: Generation, Stability and Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Horst Geckeis, Thomas Rabung, and Thorsten Scha¨fer Section 1

Methods for Actinide Nanoparticle Characterization

Scanning Transmission Electron Microscopy and Related Techniques for Research on Actinide and Radionuclide Nanomaterials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Satoshi Utsunomiya, Masashi Kogawa, Eigo Kamiishi, and Rodney C. Ewing Resonant Inelastic Soft X-Ray Scattering Spectroscopy of Light-Actinide Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 Sergei M. Butorin Characterization of Colloid-Borne Actinides by Flow Field-Flow Fractionation (FlFFF) Multidetector Analysis (MDA) . . . . . . . . . . . . . . . . . . . . 105 Muriel Bouby and Horst Geckeis Actinide Nanoparticle Characterization by Mass Spectrometry . . . . . . . . . 137 Clemens Walther Synchrotron-Based X-Ray Spectromicroscopy of Organic Nanoparticles Complexing Actinides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 Markus Plaschke, Jo¨rg Rothe, and Melissa A. Denecke

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Section 2

Contents

Modeling of Actinide Nanoparticle Structure and Behavior

From Molecules to Nanoparticles: A Computational Chemist’s Point of View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 Bernd Schimmelpfennig Theoretical Analysis of Colloid-facilitated Transport of Radionuclides by Groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 Viktor Malkovsky Section 3

Interfacial Phenomena and Formation of Actinide Nanoparticles

Nanoscale Chemistry of Uranyl Selenates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 Sergey V. Krivovichev, Vladislav V. Gurzhiy, Ivan G. Tananaev, and Boris F. Myasoedov Actinide Thin Films as Surface Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 A. Seibert, S. Stumpf, T. Gouder, D. Schild, and M.A. Denecke Sorption and Speciation of Uranium on Silica Colloids . . . . . . . . . . . . . . . . . . . 315 Dmitry N. Batuk, Andrei A. Shiryaev, Stepan N. Kalmykov, Olga N. Batuk, Anna Yu. Romanchuk, Eugeni A. Shirshin, and Yan V. Zubavichus Section 4

Environmental Behavior of Actinide Colloids and Nanoparticles

Radioactive Particles Released into the Environment from Nuclear Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335 Brit Salbu and Ole Christian Lind Effect of Redox Conditions on Actinide Speciation and Partitioning with Colloidal Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361 Stepan N. Kalmykov, Elena V. Zakharova, Alexander P. Novikov, Boris F. Myasoedov, and Satoshi Utsunomiya X-Ray Absorption Spectroscopy of Plutonium Particles at the Rocky Flats US Nuclear Weapons Production Site . . . . . . . . . . . . . . . . 377 Steven D. Conradson, David L. Clark, Christophe den Auwer, and Juan S. Lezama-Pacheco Colloid-Facilitated Transport of Plutonium at the Nevada Test Site, NV, USA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399 Annie B. Kersting and Mavrik Zavarin

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Speciation of Actinides in Granite Subjected to Tracer Studies . . . . . . . . . 413 Melissa A. Denecke, Wout de Nolf, Alexander Rack, Remi Tucoulou, Tonya Vitova, Gerald Falkenberg, Sousan Abolhassani, Peter Cloetens, and Bernhard Kienzler Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437

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Abbreviations

AEM AES AFM ALS AME An AsFlFFF BE BEI BET BF CA CCC CE CFF CLSM CRL CSH CTEM CTF CV CZE CZP DC DFT DGT DLM DLS DLVO

Analytical electron microscopy Auger electron spectroscopy Atomic force microscopy Advanced Light Source, Lawrence Berkeley National laboratory, USA Actinide Migration Evaluation Actinide Asymmetric flow field flow fractionation Binding energy Backscattered electron imaging Brunauer, Emmett, Teller (model or technique) Bright-field Cellular automata Critical coagulation concentration Counter electrode Cross-flow (ultra) filtration Confocal laser scanning microscopy Compound refractive lenses Ca-silicate hydrate phases Conventional transmission electron microscopy Contrast transfer function Cyclovoltammetry Capillary zone electrophoresis Condenser zone plate Direct current Density functional theory Diffusive gradients in thin film Diffuse layer model Dynamic light scattering Derjaguin, Landau, Verwey, Overbeek (theory)

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DOC DOE DOM dpa DU ECAFM ECP Ecorr EDS EELS EF EFTEM EPA EPR EPS EQCM ESEM ESI ESI MS ESRF EXAFS FA FBB FCS FFF FFT FIB FlFFF FT FT ICR FWHM FZP GSL GTS HA HAADF-STEM HAS HDCH HFO HLW HREELS HR-ICP-MS HRL

Abbreviations

Dissolved organic carbon U.S. Department of Energy Dissolved organic matter Displacement per atom Depleted uranium Electrochemical atomic force microscopy Effective core potentials Corrosion potential Energy dispersive X-ray spectroscopy Electron-energy-loss spectroscopies Fermi-level Energy filtered transmission electron microscopy US Environmental Protection Agency Electron paramagnetic resonance spectroscopy Extracellular polymer substances Electrochemical quartz crystal microbalance Environmental scanning electron microscopes Electrospray ionization Electrospray ionization mass spectroscopy European Synchrotron Radiation Facility, Grenoble, France Extended X-ray absorption fine structure Fulvic acids Fundamental building block Fluorescence correlation spectroscopy Flow-field flow fractionation Fast Fourier transformed Focussed ion beam Flow field-flow fractionation Fourier transform Fourier transform ion-cyclotron-resonance Full width at half maximum Fresnel zone plates Great Salt Lake Grimsel Test Site Humic acids High-angle annular dark-field scanning transmission electron microscopy Hydroxy aluminosilicate Hydrodynamic chromatography Hydrous ferric oxide High level wastes High resolution electron energy loss spectroscopy High resolution inductively coupled plasma mass spectrometry Hard rock laboratory

Abbreviations

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HS ICP-MS IR KB Kd KE KIT LA LAM LCD LEED LIBD LMM LOD LS LSLM LSV LUMO MALDI MALLS MCL MCP MDA MES ML MLEM MS MWCO m-XRF m-XRD nano-SIMS NEXAFS NMR NORM NP NSLS

Humic substances Inductively coupled plasma mass spectrometry Infrared Kirkpatrick-Baez (mirrors) Distribution coefficient Kinetic energy Karlsruhe Institute of Technology Laser-ablation Linear additive model Ligand charge distribution Low-energy electron diffraction Laser-induced breakdown detection Low molecular mass Limits of detection Light scattering Laser scanning luminescence microscopy Linear sweep voltammetry Lowest unoccupied molecular orbitals Matrix-assisted laser-desorption ionization Multiple-angle laser light scatterings Maximum contaminant level Multi-channel plates Multi detector analysis Molecular environmental science Monolayers Maximum likelihood expectation maximization Mass spectrometry Molecular weight cut-off Micro- X-ray fluorescence analysis Micro- X-ray diffraction Secondary ion mass spectrometry with nanoscale resolution Near edge X-ray absorption fine structure Nuclear magnetic resonance Naturally occurring radioactive material Nanoparticle National Synchrotron Light Source, Brookhaven, New York, USA Nevada Test Site, Nevada, USA Polyacrylic acid Primary building units (6,6)-phenyl C61 butyric acid methyl ester Photon correlation spectroscopy Point of zero charge Pseudo potentials

NTS PAA PBU PCBM PCS pHpzc PP

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m-PIXE PNBU QP RBS RE Rf RF RFETS RHEED RI RIMS RIXS RT RTG RW SAED SANS SAXS SBU SCM SEC SEM SEM-EDX SEXAFS SF SIMS SKB SLS SNF 2SPNE SC/CE SR SRS SSCP STM STEM STS STXM SWIFT SymFlFFF TDA TDS TEM

Abbreviations

Micro-particle (or proton) induced X-ray emission Prenucleation building units Quadrupol Rutherford backscattering spectrometry Reference electrode Retardation factor Radiofrequency Rocky Flats Environmental Technology Site Reflection high energy electron diffraction Refractive index Resonance Ionization Resonant inelastic x-ray scattering Room temperature Radioisotope thermoelectric generators Radioactive waste Selected area electron diffraction Small angle neutron scattering Small angle X-ray scattering Secondary building units Surface complexation modeling Size exclusion chromatography Scanning electron microscopy Scanning electron microscopy combined with energy-dispersive X-ray spectroscopy Surface extended X-ray absorption fine structure Sector field (analyzers) Secondary ion mass spectrometry Swedish Nuclear Fuel and Waste Management Company Swiss Light Source Spent nuclear fuel Two-site protolysis, nonelectrostatic surface complexation and cation exchange model Synchrotron radiation Savannah River Site Scanning stripping chronopotentiometry Scanning tunneling microscopy Scanning transmission electron microscopy Semipalatinsk Test Site Scanning transmission X-ray microscopy Stored-waveform inverse-Fourier-transform Symmetric flow field flow fractionation Taylor dispersions analysis Thermal diffuse scattering Transmission electron microscopy

Abbreviations

TEM/EDX TENORM TFF TIMS TOF TRLFS TXM UF UHV URL UPS UV UV/Vis VLS WE WIPP XANES XAS XPS XRD XRM XSW YAG

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Transmission electron microscopy coupled to X-ray energy dispersive spectroscopy Technologically enhanced NORM Tangential-flow filtration Thermal ionization mass spectrometry Time-of-flight Time-resolved laser fluorescence spectroscopy Transmission X-ray microscopy Ultrafiltration Ultra-high vacuum Underground rock laboratory Ultraviolet photoelectron spectroscopy Ultraviolet Ultra violet/visible Variable-line-spacing-grating (spectrograph) Working electrode Waste Isolation Pilot Plant X-ray absorption near edge spectroscopy X-ray absorption spectroscopy X-ray photoelectron spectroscopy X-ray diffraction X-ray microscopy X-ray standing wave Yttrium aluminum garnet (laser)

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Actinide-Nanoparticle Interaction: Generation, Stability and Mobility Horst Geckeis, Thomas Rabung, and Thorsten Sch€afer

Abstract Actinide ions are widely considered immobile under environmental conditions relevant to their disposal notably under reducing conditions prevalent in subsoil systems. Colloid formation is, however, known to increase their mobility. Observations of this in environmental systems are regularly reported. Different processes may lead to actinide colloid formation, by either generation of polymeric oxide/hydroxide nanoparticles or sorption to already existing or neo-formed ground water colloids. In order to assess actinide mobilization by colloidal species, the cascade of individual colloidal processes under given geochemical conditions must be considered and quantified: colloid formation, actinide–colloid interaction, colloid stabilization and migration. This chapter describes and discusses actinide colloid reactions with a focus on the underlying mechanisms.

1 Introduction Naturally occurring or “environmental”colloids/nanoparticles can be defined as solids of organic or inorganic nature in the size range from ~1 nm to ~1 mm (upper size limit depending on their density) that remain suspended in water. Inorganic colloids/nanoparticles are formed by chemical alteration or physical erosion of minerals, or by direct precipitation from ground water, and typically comprise silica, clay minerals, calcite or metal-oxyhydroxides. Two types of

H. Geckeis (*) and T. Rabung Karlsruhe Institute of Technology (KIT), Institute for Nuclear Waste Disposal (INE), P.O. Box 3640, 76021 Karlsruhe, Germany e-mail: [email protected] T. Sch€afer Karlsruhe Institute of Technology (KIT), Institute for Nuclear Waste Disposal (INE), P.O. Box 3640, 76021 Karlsruhe, Germany Freie Universit€at Berlin, Institute of Geological Sciences, Hydrogeology Group, 12249 Berlin, Germany

S.N. Kalmykov and M.A. Denecke (eds.), Actinide Nanoparticle Research, DOI 10.1007/978-3-642-11432-8_1, # Springer-Verlag Berlin Heidelberg 2011

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inorganic nanoparticles are usually distinguished. The so-called intrinsic- or eigencolloids/nanoparticles consisting essentially of polymerized complexes of a particular element (e.g., Pu(IV)-polymer) formed by condensation of hydrolyzed Pu(IV) ions and consisting of cations linked by anions. These types of polymeric actinide species have recently attracted attention, as they may dominate the solubility of the tetravalent actinides and play a significant role in the complex redox chemistry of plutonium (Neck et al. 2007a; Soderholm et al. 2008) (see, e.g., Chaps. 5 and 13). The carrier- or pseudo- colloids/nanoparticles consist of mineral fragments of crystalline or amorphous solids to which a particular element/radionuclide may be attached. Organic nanoparticles may comprise fragments of degrading organic material, or they may be organic macromolecules (i.e., humic or fulvic acids) or microbes (biocolloids). Organic materials, especially humic and fulvic acids may form coatings on inorganic nanoparticles, increasing their electrostatic stability. Numerous publications have demonstrated that the classical two phase flow concept of transport (stationary phase: sediment; mobile phase: ground water) has to be expanded to include a third phase, namely the nanoparticles, which are ubiquitous in aquifer systems (Kretzschmar and Sch€afer 2005; McCarthy and Zachara 1989; Wilkinson and Lead 2006). Neglecting the nanoparticulate phase in ground water systems can drastically underestimate the mobility of strong sorbing contaminants (e.g., plutonium) (Kersting et al. 1999; Kim 1994; Kim et al. 1984). The discussion of clay colloids washed out from the bentonite barrier in a granitic nuclear repository due to low salinity glacial melt water intrusion (Neretnieks and Liu 2006) has focused new attention to this issue. Geochemically or hydraulically disturbed systems especially might generate a high concentration of colloidal phases, and therefore can enhance the mobility of strong sorbing contaminants (Ryan and Gschwend 1994). On the other hand, colloid destabilization via aggregation can also lead to an additional retention mechanism for strong sorbing contaminants. Transport in far-field environments/geological formations has to take into account saturated and unsaturated flow regimes (Robinson et al. 2003). Nanoparticle mobilization and transport in unsaturated host rocks and from soils to the ground water table (vadose zone) is an important research topic, which changes nanoparticle migration mechanism (DeNovio et al. 2004). Such effects must be considered, e.g., in the far-field system of the U.S. Department of Energy (DOE) Yucca Mountain (Nevada) site, the underground waste tank leakages at the U.S. DOE Washington State Hanford Site (Zhuang et al. 2007) and potential gas migration pathways. Understanding colloid transport in unsaturated media is complicated by the presence of dynamic air–water interfaces and the increasing discontinuity of waterfilled pores with decreasing water content. Additional mechanisms of nanoparticle retention have been suggested such as film-straining and deposition of nanoparticles onto the air–water interface. Attachment of actinides to colloids does not necessarily mean high mobility. Colloid attachment to geosphere surfaces, colloid agglomeration, sedimentation and filtration in nanoporous rock such as clay rock, and actinide desorption from colloids followed by sorption to minerals contribute to actinide retention even in the presence of colloids.

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In general, the importance of colloidal phases or nanoparticles on transport processes depends on (a) their presence, (b) their mobility and stability and (c) the slow reversibility or “irreversibility” of metal/radionuclide interaction with these nanoparticles, which are discussed in detail below.

2 Background Nanoparticles in Geological Systems The sampling of colloids/nanoparticles in ground water systems is not a trivial issue: a number of artefacts such as oxygen intrusion can bias the sampling procedure and, consequently, the reliable measurement of background nanoparticle concentration. The exact determination of nanoparticle background concentration is motivated by the fact that this concentration will give an estimation of the maximum transport enhancement for strongly sorbing tracers. In porous and fractured rocks the sampling methology is well documented (Backhus et al. 1993; Barcelona et al. 2005; Degueldre et al. 1996b). A general procedure for low-flow passive sampling technique has been established for different geological formations, as documented in, e.g., an US Environmental Protection Agency (USEPA) workshop summary (Puls 1995). Discussions on the advantages of different analytical techniques that can be used for background nanoparticle sampling are also found elsewhere (Barcelona et al. 2005; Nilsson et al. 2008). Much progress has also been made in the field of analytic development concerning the detection of nanoparticles (see other contributions in this book). The community clearly benefits from developments made, especially in the field of nanoparticle size distribution analysis (e.g., via laser-induced breakdown detection, LIBD) and flow-field flow fractionation (see Chap. 4), and the possibility to detect size dispersion/chromatography effects in nanoparticle migration experiments (Delos et al. 2008; Walther et al. 2006).

2.1

Inorganic Nanoparticles

Different colloid field studies are available in the literature. Degueldre et al. (1996a, b, 2000) collected colloid data and derived stability criteria. A mobile LIBD equipment (Hauser et al. 2002) has been used in field investigations at the Grimsel Test Site, in the Swedish site investigation program and other site investigations (e.g., the Ruprechtov site, Czech Republic) and provided detailed information on inorganic nanoparticle concentration in several observation boreholes and correlated these to geochemical parameters. The data show that inorganic nanoparticle concentration in advective transport dominated far-field environments (crystalline and rock salt overburden) is mostly limited to concentrations